Field of the Invention
This invention relates generally to the field of wireless communications; and more particularly, to Multiple Input Multiple Output (MIMO) antenna implementations capable of robust multi-band operation for use in wireless communications.
Related Art
Current and future communication systems will require improved MIMO antenna systems capable of operation over multiple frequency bands. Isolation between adjacent elements as well as de-correlated radiation patterns will need to be maintained across multiple frequency bands, with antenna efficiency needing to be optimized for the antenna system.
Commonly owned U.S. Pat. No. 7,911,402, issued Mar. 22, 2011, describes a beam steering technique wherein a single antenna is capable of generating multiple radiating modes; the contents of which are hereby incorporated by reference. This is effectuated with the use of offset parasitic elements that alter the current distribution on the driven antenna as the reactive load on the parasitic is varied. This beam steering technique where multiple modes are generated is referred to as a “modal antenna technique”, and an antenna configured to alter radiating modes in this fashion will be referred to herein as an “active modal antenna”.
Commonly owned U.S. application Ser. No. 13/227,361, filed Sep. 7, 2011, describes a receive diversity antenna utilizing an active modal antenna as described in the '402 patent, wherein a single modal antenna can be configured to generate multiple radiating modes to provide a form of switched diversity; the contents of which are hereby incorporated by reference. The benefits of this technique include reduced volume in the mobile device for a single antenna instead of a two antenna receive diversity scheme, reduction in receive ports on the transceiver from two to one, and the resultant reduction in current consumption from this reduction in receive ports.
With MIMO (Multiple Input Multiple Output) systems becoming more prevalent in the access point and cellular communication fields, the need for two or more antennas collocated in a mobile device or small form factor access point are becoming more common. These groups of antennas in a MIMO system need to have high, and preferably, equal efficiencies along with good isolation and low correlation. For handheld mobile devices the problem is exacerbated by antenna detuning caused by the multiple use cases of a device: hand loading of the cell phone, cell phone placed to user's head, cell phone placed on metal surface, etc. For both cell phone and access point applications, the multipath environment is constantly changing, which impacts throughput performance of the communication link.